Vibratory reed device and system employing the same



April 22, 1958 w.A P. FOSTER ETAL 2,831,937

VIERATORY REED DEVICE AND SYSTEM EMPLOYING THE SAME Filed Feb. 17, 1954United States Patent() VIBRATORY REED DEVICE AND SYSTEM EMPLOYING THESAME William P. Foster, Lansdowne, Pa., and Charles A. Richardson,Linwood, N. J., assignorsto James G. Biddle Co., Philadelphia, Pa., acorporation of Pennsylvania Application February 17, 1954, Serial No.410,857

3 Claims. (Cl. 200`91) This invention relates to vibratory reed devicesand to systems employing a plurality of such devices tuned to differentfrequencies. Whilev the invention is applicable generally to suchdevices and systems, it is especially applicable to resonant reed relaysand systems employing the same. Accordingly, the invention will bedescribed herein with reference to such specific application. However,it is to be understood that in the broader aspect of the invention theresonant reed relay and relay system are to be regarded only asexemplary of vibratory reed devices and systems.

A resonant reed relay, like other vibratory reed devices, commonlyemploys at least one cantilever type resonant reed and an associateddriving means and, preferably, such relay has `a primary reed and asecondary reed extending in parallel relation from a common mount. Theresonant frequency of vibration `is directly proportional to thethickness of the reed and is inversely proportional to the square of thefree length of the reed.

In prior constructionsof resonant reed relays the driving point has beenlocated at the tip of the reed because the sensitivity is greatest atthat point. In systems in which such relays are commonly employed,onepractice t has been to maintain the lengths of the reeds constant andly requires increased input. This objection is partiallyy met byoperating thereeds at reducedamplitude, and partially by increasing themagnetic bias which increases the driving force. However, if the inputcurrent is to'be maintained at a constant level, the necessaryadjustments of amplitude and bias cause manufacturing difficulties.

One object of the present invention is to overcome the above-mentionedobjection.

ing at the highest frequency, and by tuning the other relays of theseries to lower frequencies by increasing the reed lengths whilemaintaining the driving point at the same distance from the reed mount.according to the present invention the relays are char- `acterized inthat the reeds of the respective relays are of the same width andthickness but of different free lengths to operate at differentfrequencies within a predetermined frequency range, and the drivingmeans of all of the relays are located at the same point along the freelengths of the reeds.

A further feature of the present invention is that the contact gapspacing is"approximately constant for allk relays in a series, and thecontact gap is located at the same distance from the reed mount as thedriving point.

Thus, at the critical contact-making instant, the `reed amplitude at thedriving point is` approximately constant for This is achieved bylocating the driving point at the reed tip only inthe relay operat-Thus, in a system all relays of a series. It has been found that thishas tho effect of providing substantially uniform responsecharacteristics in the series of relays.l

Another object of the present invention is to provide an improvedvibratory reed device which is highly etlicient in operation and whichhas desirable operating characteristics.

A further object ofthe invention is to provide a resonant reed relaywhich is of simple compact construction, and which is economical tomanufacture and easy to adjust. j

Other objects and features of the invention will be apparent from thefollowing detailed description with reference to the accompanyingdrawings, in which:

Fig. 1 is an elevational view of a resonant reed relay constructedaccording to the present invention, with the casing or housing brokenaway to show the parts, and with certain elements broken away and shownin section for the purpose of illustration;

Fig. 2 is an elevational View taken from the right sidev of Fig. 1, withthe casing broken away;

Fig. 3 is a cross-sectional view taken on line 3 3 of Fig. 1;

Fig. 4 is a longitudinal sectional view taken centrally through thedevice on line 4-4 of Fig. l;

Fig. 5 isa bottom view of the device;

Fig. 6 is a cross-sectional view taken on line 6-6 of Fig. l; n

Fig. 7 is a perspective view of the assembly which is contained withinthe casing; l

Fig. 8 is a graph showing the representative response curve fora relayconstructed according to the invention; and f Fig. 9 is a diagrammaticillustration of a frequency responsive relay system according to thepresent invention.

Referring to the construction of a preferred embodiment of a resonantreed relay according to the present invention, as illustrated in Figs. lto 7, there is provided an elongate metal casing or housing 10 which ispreferably of cylindrical shape and which is closed at its upper end andhas an opening at its lower end to receive a closure member 11 which isalso preferably formed of metal. The relay assembly containedwithin thecasing 10 is supported as a unit by the closure member 11 which thusserves a dual purpose, i. e. both as a closuremeans for the casing andalso as a support for the internal relay assembly.

In the preferred form illustrated, the relay assembly comprises agenerally U-shaped support 12, also preferably formed of metal, having apair of spaced arms 13 and 14 extending upward from the bottom portion15 whichhas an 'extension 16 and is provided with a central threadedpassage 17 to receive an attachment screw 18. As may be seen in Fig. 4,the closure membery 11 has a central aperture 19 to receive the screw18, the aperture preferably being shaped to provide counter-sinking ofthe screw head which may be sealed by solder 20 afterv the device'hasbeen assembled. The supported assembly further comprises a generallyU-shaped reed structure formed of magnetic material, e. g. steel,`andhaving a base 21 and a pair of reeds 22 and 23extending upward from thebase in substantially parallel relation to one another. The generallyU-shaped reed structure is disposed at right angles to the U-shapedsupport 12 withv the base 21 interposed between the arms 13 and 14 ofthe support. As may be seen in Figs. l, 2 and 4, the

apertures ..25 to ,ac ccmrncdate the screws, the apertures beingenlarged at their outer portions to accommodate insulating washers 26.The screws 24 threadedly engage apertures in the base 21 of the U-shapedreed structure. An insulating sheet V26a is interposed between base 21and arm 14.

Referring more particularly to the reed structure, the base 21 is in theform of a metal block, and the reeds 22 and 23 are in the form of atmetallic strips secured to the base 21 as by silver soldering orbrazing. The reed 22 is the primary reed and it carries an electricalcontact l27 secured thereto as by spot welding. The reed 23 is asecondary reed which serves simply to provide a balanced twin reedstructure. A dummy contact 28 is secured to reed 23, as by spot welding,to better balance the twin reed structure. Associated with the primaryreed 22 is a resilient contact arm 29 carrying an electrical contact 30which is cooperable with the contact 27. Arm 29 has a lateral extension31 by which it is mounted on arm 13 of the rigid support 12 by means ofscrews 32, being insulated from the metal support by insulating strips33 and 34 (see Fig. 6). Reed 22 is electrically connected to one of anumber of contact pins 35 through a connection 36. The contact pins 35are insulated from the metallic closure member 11 by extending throughfused glass seals 37. The contact arm 29 is also connected to one of thepins 35 through a connection 38. The pins 35 are similar to theprojecting contact pins of an electron tube, the device being adapted tobe plugged into a socket in the manner of an electron tube. The contacts27 and 30 serve to control a controlled circuit, in response toactuation of the reed 22 by the driving means now to be described.

The driving means comprises an electrical coil 39 which is interposedbetween the reeds 22 and 23 and is so oriented that its axis lies in thedirection of vibration of the reeds. The coil is formed of insulatedwire wound on an insulating spool 40 to provide a coil unit which isheld by the arms 13 and 14 of the rigid support 12. To this end the arms13 and 14 are machined to provide recesses 41 and 42 in order that thecoil unit may be inserted and embraced by the support arms. The coilunit is held securely in place by means of screws 43 and 44 on oppositesides of the support arms with their heads engaging the opposed faces ofthe coil spool 40. Within the coil spool is a permanent magnet coil 45which not only provides a magnetic core for the coil but is utilizedduring tuning as hereinafter described. ln the form i1- lustrated, thepermanent magnet core is of square crosssectional shape and it litssnugly within the spool 40 so as u to remain stationary therein. Theends of the coil 39 are connected respectively to two of the contactpins 35 by means of conductors 46 and 47.

It will be seen from the foregoing description that the entire internalstructure of the relay is assembled as a unit with all of the componentelements mounted on the common rigid support 12 which in turn is securedto and supported by the closure member 11. As may be seen in Figs. l, 2and 4, the lower end of the metallic casing 10 is formed to provide aninternal shoulder 48 to seat the closure member 11, and the member 11 isheld within the lower end of the shell-like casing by means of a ring ofsolder 49.

In constructing and assembling the above-described resonant reed relay,the support 12 is first assembled to the member 11. The reed block 21and the reeds 22 and 23 are assembled by silver soldering or brazing,after which the reed assembly is heat treated in order to provideoptimum characteristics of the steel. The reed contacts are then spotwelded to the reeds at the proper location, and the assembly is tuned toa predetermined frequency in a special Xture designed to vibrate theblock. The preliminary adjustment is made by shortening the reed length,and the nal adjustment is made by weighting the reed tips slightly,using solder. The coil and vmagnet assembly comprising coil 39 andmagnet 45 is then charged to a predetermined level and is assembled tothe support 12. The reed assembly is then mounted on the support 12, andthe contact arm 29 is also mounted thereon. At this point in theassembly the contact gap is adjusted by bending the arm 29 to provide apredetermined gap spacing between the contacts 27 and 30. Theabovedescribed electrical connections to the contact pins are then made.At this point the magnet 45 is demagnetized by applying an alternatingcurrent of suiiicient magnitude to the coil 39. This reduces themagnetic ux so that the reed frequency increases to a finalpredetermined value which is somewhat different than the valuepredetermined for the original reed tuning. Finally, the assembly isinserted in the casing and the latter is hermetically sealed by applyingthe ring of solder 49.

Figure 8 shows a representative response curve for a relay constructedaccording to this invention. In order to determine this curve, an A. C.signal is applied to the driving coil and is maintained at somearbitrary level, and its frequency is changed from outside the bandtoward the nominal frequency. An ohmmeter, or suitable signal device, isused to determine when the contacts close. At signal levels within acertain range there will be two contact close points; one as thefrequency is varied upward toward the nominal frequency, and the secondas the frequency is varied downward toward the nominal frequency. Ineach case the contacts must be open as the frequency starts to sweep.This procedure is repeated for different signal levels to determine thepoints of the curve.

Fig. 9 shows a frequency selective relay system ernploying a series ofresonant reed relays constructed according to the present invention. Inthe illustrated system the number of relays chosen for the purpose ofillustration was arbitrarily selected as four, the relays beingdesignated by reference numerals 50 to 53. The relays arediagrammatically illustrated, and it is to be understood that they areof the character illustrated in Figs. 1 to 7 and described above. Therelays are characterized in certain novel respects which will now beexplained.

In earlier designs of reed relays the driving point has been placed atthe tip of the reeds because the sensitivity is greatest at this point.In a series of relays having different frequencies this practice resultsin diiferent characteristics among the relays in the series unlessspecial precautions are taken. Where frequency is increased by makingthe reeds thicker, the driving force required to produce the sameamplitude is greater. This is partially oifset by operating the reeds atreduced amplitude, and partially by increasing the magnetic bias whichincreases the driving force. If the driving coil input current is to bemaintained at a constant level the necessary adjustments of amplitudeand bias introduce manufacturing difficulties.

According to this invention, the driving point is at the tip of thereeds only for the highest frequency in the series. As frequency isreduced by increasing reed lengths while maintaining the width andthickness constant, the driving point remains fixed and is, therefore,applied at some fraction of the reed length, which becomes increasinglysmaller as the reed length increases.

A further feature of the present invention lies in the contact gapspacing, which is designed to be constant for all relays in a series.This contact gap is located at the same distance from the reed clamppoint as the driving point. Thus, at the critical contact making instantthe reed amplitude at the driving point is constant for all relays of aseries. It has been found that this has the effect of providing asubstantial improvement in the uniformity of the response curvecharacteristics of a series of relays covering a range of frequencies asgreat as 4 to l in the lower audio frequency spectrum.

f A further feature of this invention is the arrangement ofthe drivingmeans and the support for it and the reeds.

In a reed relay as small as those contemplated in this invention,driving at a point isnot possible in the strict sense of the word. Thebest that can be done is t0 concentrate the driving forces within asmall area about the desired point. EvenL when this is done there is anappreciable distributed driving vefect because of the physical size ofthe drive coil and the close spacing of the twin reeds. Two distinctdriving effects are present in all the known driving methods. The firstis the reaction between the drive coil and the reeds. The second is thereaction of one reed on its twin. In some types of drive the reeds repeleach other while being attracted toward a central driving system. Forexample, if the pole of a permanent magnet is placed between the reedsand acoil is wound around the reeds, the increase in ux that causes thereeds to be attracted to the permanent magnet also causes the reeds torepel each other. This results in a loss of etliciency and reduceddiscrimination between response at the design frequency and response athalf the design frequency.

The drive employed in this invention makes use of ar coil wound aroundthe permanent magnet and oriented between the reeds in such a way thatan increase in ux causes an attraction of the reeds toward the center,and the reeds are so polarized that they attract each other. Thus, beingin phase, the two effects add and give increased eiciency and betterdiscrimination between response at the design frequency and response athalf the design frequency. Because the coil is wound around the magnetit is also possible to magnetize using the coil. Thus, the magnetstrength may be adjusted by applying appropriate signals to the externalterminals. Since frequency can be adjusted by magnetic field intensityit is possible to adjust frequency after the relay is assembled in itscasing and sealed. The reeds are tuned to some frequency about a halfpercent above the nominal frequency. The relay may then be assembled andsealed after which a magnetizing signal isapplied tothe coil bydischarging a capacitor into it or by other means of applying a short,high intensity current pulse. The midband frequency of the relay ismeasured by locating the lowest point of the response curve (see Fig.8). This measurement must be made without increasing the applied signalmore than necessary. The frequency will be lowered as a result ofmagnetizing. An alternating signal of proper level is then applied inorder to demagnetize the magnet and bring the frequency back-up to itsnominal value. The determination of the proper demagnetizing signal isdone experimentally in steps of increasing level similar tothe manner inwhich a precision resistor is adjusted by trimming wire.

While the invention has been described with particular reference to thedrawing disclosure, it is not limited thereto but contemplates suchmodifications and further embodiments as may occur to those skilled inthe art.

We claim:

1. In a vibratory reed device, a stationary mounting means, a primaryreed and a secondary reed secured to and extending from said mountingmeans in opposed spaced relation to one another, a straight magneticcore permanently magnetized to provide a magnetic bias and extendingtransversely between said reeds, a coil wound about said core wherebymagnetizing currents may superimpose a fluctuating magnetic field on themagnetic bias,

and means tixedly mounting said coil and core in relation to said reeds.

2. A resonant reed relay, comprising an elongate metal casing or housinghaving an opening at one end, a closure member at the said end of thecasing, Support means within said casing secured to said member, areed-supporting block within said casing secured to saidsupport means, aprimary reed and a secondary reed within said casing extending from saidblockin opposed spaced relation to one another,.a contact on saidprimary reed, a fixed arm secured to said support means and disposedadjacent to said primary reed within said casing, a contact armcooperable with said rst contact, a straight magnetic core permanentlyrnagnetized to provide a magnetic bias vand extending ytransverselybetween said reeds, a coil wound about said core whereby magnetizingcurrents may superimpose a fluctuating magnetic field on the magneticbias, andmeans xedly mounting said corel and core on said support means.

3. A resonant reed relay, comprising an elongate metal casing or housinghaving an opening at one end, a closure member at the said end of thecasing, support means within said casing secured to said member, areed-supporting block within said casing secured to said support means,a primary reed and a secondary reed within said casing extending fromsaid block in opposed spaced relation to one another, contactscontrolled by said primary reed, a straight magnetic core permanentlymagnetized to provide a magnetic bias and extending transversely betweensaid reeds, a coil wound about said core whereby magnetizing currentsmay superimpose a uctuating magnetic field on the magnetic bias, andmeans fixedly mounting said coil and core on said support means.

ReferencesCited in the tile of this patent `UNITED STATES PATENTS GreatBritain Apr. 12, 1950 UNITED STATES PATENT @ENCE CERTIFICATE 0F CORBCTNPimm; NQ.- 2,831,937 April 22?, 1958 v Willian P* Fester It i herebycertified that error appears in Ehe prmed specification of the abovenumbered patent requiring correction and that the said Leters Patentshould read as corrected below.

.Column lima 2l, before "rmf insert a on said 4 lnef 26,; car "core"read `--f'- cnil Signed' r-md sealed this 5th .day of August l9`58(SEAL) Angst:

KARL H, AXLINE l y ROBERT C. WATSN Attesting Ofcer y 'I Cammissioner ofPatents UNITED STATES PATENT @FFME CERTIFCATE F CRRECN mmm Nm 2,831,937April 2z, w58

Willie-.m Pm Fuster ai: alf It ir hereby cer-bifd 'that error appaars inme printed specaton Gf. the above numbeed patent requiring correctianand that the said Liiers Patent should read yas corrected blow.

.001mm lilik? 2l, before "am" insert sa on said line Ef im "core" e'ad,.L. mi; .ma

Signed' and saled this 5th day of August lQ (SEAL) ttst:

KARL 'H1 AXLINE l HBERT WA'N Attesting Ocer Cwmmissianer @E Fammi;

